What's necessary to setup automated bounce processing?

Specify a separate mail account in envelope's 'MAIL FROM:' header than in 'From:' header. Then most of bounces will go to the first account, while replies to the second account. (About 1% of bounces will still come to the same account as replies, because of bad implementations of SMTP servers.)

To set the envelope header you will need JavaMail v1.2 or newer, set it using mail.smtp.from property, as is described in another answer.